shark activity 1

8/6/2019 Shark Activity 1

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Activity 1

Morphology of a Reef Shark

I. Introduction

Cartilaginous fishes, which include sharks, rays and chimeras, are primitive fishes with biting jaws, paired appendage, and a tough, leathery skin that is usually covered with placoid

scales. The fishes with these characteristics belong to Class Chondrichthyes of the subphylumVertebrata (Lytle and Wodsedalek, 1987).

The sample that has been used in this experiment is the White-tip Reef Shark

(Triaenodon obesus.). This shark is under the family Carcharhinidae and is commonly found onthe indo-pacific coral reefs. It can be easily recognized by its slender body, broad head tip and a

white-tip dorsal and caudal fin. During the day, this shark spends much time on caves.

II. Objectives

This laboratory experiment titled ³External Morphology of the Shark´ focuses on the

examination of the different external parts of the White-tip Reef shark. The following objectiveswere formulated to guide the students:

1. Identify the different external morphology of the white-tip reef shark;

2. Describe the functions of each part that have been identified; and

3. Differentiate the ventral and dorsal scale of the shark.

III. Methodology

A. Preparation of materials and samples

Secure a fresh shark from the market and wash with running water before

use. Prepare 2 sharp scalpels, 2 pairs of sharp scissors and a mat. Clean your work area before placing the shark horizontally on the mat at the work area. Borrow

one light microscope and 2 glass slides for the Procedure in letter C.

B. Parts Identification and documentation

Observe the external anatomy of the shark and locate the different positions of the body (anterior, posterior, ventral, dorsal, etc.) and the different

planes (transverse plane, sagittal plane). Identify the different parts located indifferent regions of the body and in different positions. Refer to a textbook to



validate the answers. Illustrate the ventral, dorsal and lateral positions of thesharks¶ body. (Note: Document if necessary)

C. Shark Skin viewed under the Microscope

Cut a small thin fragment of skin, 1 fragment from the ventral side and 1form the dorsal side of the body using a scissor or scalpel. Place each fragmentson separate glass slides, the scales should be facing upward. Use a light

microscope to view each scale sample under the Low Power Objective (LPO) andunder High Power Objective (HPO). Note the form and coloration of the skin

under both samples and illustrate. (Note: if the fragment cannot be viewed under HPO, do not force)

D. Removing the Shark skin

Make an incision at the ventral median position of the body. (Note: skin is

thinner at the ventral than the dorsal position). Cut laterally upward and/or downward and expose only the ventral muscles and not the internal organs.

Caution should be observed because the skin is attached to the muscles. At anyrate and at any way, provided that the muscles are intact and have less damage,

remove the skin except those in the tail and fins.



V. Discussion

Sharks are commonly used as a representative of other Chondrichthyes when comparing

their morphology, physiology and anatomy to other forms of vertebrates such as the bony fishesand other higher forms of vertebrates. Species under the class Chondrichthyes, share similar

characteristics such as having a cartilaginous skeleton as compared to the bones of other fisheswhich are included in the class Osteichthyes.

In this activity, the students were able to observe the different external characteristics or

parts of the White-tip reef shark; identified the physiology of each external morphologicalcharacteristics of the shark and compared the scales found at the ventral and dorsal of the sharks¶

skin.

The different parts identified are: Head, Eyes, Nares, Mouth, External gill slits, Pectoralfins, Pelvic fins, Anterior and posterior dorsal fins, Fin spines, Lateral line canal, Caudal fin,

Ventral-anal fin, Ampullae of Lorenzini, Cloaca, Claspers and the Epidermis. The shark sampledoes not have spiracles which are usually located at the posterior of both eyes. The presence of

the ventral-anal fin was observed which is not present in dogfish sharks. Based from the shark sample, the following descriptions were made and have been verified in other references.

The head is the most anterior part of the body, almost flattened and triangular in shape(Macahia & Nicart, 2002) which houses the different parts such as the eyes, nares or external

nostrils, and mouth. The eyes are found lateral to the head and functions as the visual tool for theshark. According to Macahia and Nicart (2002), the eyes are oval shape and do not have an

upper and lower eyelids. The mouth and nostrils are situated ventral to the head. The nostrils or nares have a flap of skin and is located anteroventral to the rostrum. The rostrum, according to

Macahia and Nicart (2002), is the ³pointed anterior end of the head´. The mouth is used for respiration aside from eating food. The head also have numerous small spores located dorsal and

ventral to the head, which is known as the Ampullae of Lorenzini. According to Wischnitzer (1972), the Ampullae of Lorenzini are special sensory endings used as thermoreceptors and

mechanoreceptors.

The external gill slits as observe were 5 vertical openings each sides lateral to the headand anterior to the pectoral fins. These are mainly used for respiration. According to Wischnitzer

(1972), the Pectoral fins located ventrolaterally behind the gill slits are larger compared to the pelvis fins that are located ventrolaterally at the caudal end of the trunk. As observed there were

the presence of the anterior dorsal fin and the posterior dorsal fin. These fins have a whitecoloration in each of its tip. A fin spine is present and is located posterior to each of the said

dorsal fins but as compared to the dogfish shark in the manual, the fin spines are anterior to thedorsal fins. The ventral-anal fin found on the white-tip reef shark is absent in the dogfish sharks.

The caudal fin or the tail of the shark has two lobes the dorsal lobe and the ventral lobe. Thestudents noticed that the dorsal lobe is much longer than the ventral lobe. The major function of

the fins is to aid locomotion especially the tail.

From the head to the posterior of the trunk, a linearly arrange minute openings called thelateral canal is very sensitive that it can detect stimulus from the environment or waters to aid the

shark¶s locomotion (Wischnitzer, 1972).



Claspers are modified copulatory organs and are found median to the pelvic fins(Wischnitzer, 1972). This indicates that the shark sample is a male white-tip reef shark. The

cloaca was also visible and is median and proximal to the claspers. This serves as the opening for three systems of the body, the urinary system, reproductive system and the digestive system

(Kardong, 2002).

The Epidermis of the shark is darker and thicker on the dorsal, while whiter and thinner

on the ventral. The dark coloration of the epidermis is due to the presence of melanophores. Theadaptation of having the back filled or covered with melanophores and less in the belly, is

because it allows to shark to camouflage itself underwater; in the sense that they are less visiblefrom above and from below the ocean (Wischnitzer, 1972). The sharks¶ scales are called placoid

scales which may vary from different shapes, but are similarly rough and strong. Viewing thescales under the microscope is somehow difficult because the skin is an opaque material in that

the light cannot pass through. The dorsal scales as observed are darker while the ventral scalesare lighter. Due to the problem, further magnification could not yield a detailed illustration of the

scales¶ characteristics.

VI. Conclusion

Sharks are classified under the Class Chondrichthyes while other bony fishes are under

the Class Osteichthyes. They differ mainly in their skeletal components and also theinteguments, Sharks have cartilaginous skeletons and are covered with placoid scales while the

latter have bony skeletons.

The visible external morphology of the male white-tip reef shark are as follows: TheHead, Eyes, Nares, Mouth, External gill slits, Pectoral fins, Pelvic fins, Anterior and posterior

dorsal fins, Fin spines, Lateral line canal, Caudal fin, Ventral-anal fin, Ampullae of Lorenzini,

Cloaca, Claspers and the Epidermis. There are structures which differ from the White-tip reef sharks and the dogfish sharks such as the presence of the Ventral-anal tail and white-tipcoloration of both dorsal fins on the White-tip reef shark are absent in the dogfish sharks. The

spiracle is absent in the sample used and the fin spines are located posterior to the dorsal fins,which differ to the dogfish shark which have spiracles and its fin spines are anterior to the dorsal

fins.

The dorsal epidermis is darker in color due to the melanophores, while the ventralepidermis is light in color due to the absence of the melanophores. Different parts of the placoid

scales were observed only under 100x magnification. Further magnification would yield a darker and unclear image, due to the thickness of the skin where light cannot pass through.



VIII. Reference

Books

Macahia, A.H., M.S. & Nicart, M.R., M.S. (2002). C omparative anatomy of

vertebrates:Laboratory manual. Metro Manila: Navotas Press

Kardong, K.V., PhD (2002). Vertebrates: C omparative anatomy, function, evolution, 3rd

Ed. USA: McGraw-Hill Companies, Inc.

Wischnitzer, S., W.H. (1972). Atlas and dissection guide for comparative anatomy, 2nd

Ed. San Francisco: Freeman and Co.

Lytle, C.F. & Wodsedalek, J.E. (1987). General zoology: Laboratory guide, 10th

Ed.

Internet

Placoid scales. Retrieved from preservearticles.com, on July 5, 2011.

Name: Josephine Ivy T. Jumala

Ralph Renon T. Casamayor



Questions

1. How are placoid scales form?

Placoid scales are structures found on the epidermal part of the Cartilaginous fishes,which are also structurally homologous with the vertebrate teeth. According to the

preservearticles.com, placoid scales are derived from the dermis and partly from the epidermis.The dermal papilla grows upwards pushing the epidermis, and then it takes the shape of a basal

plate and spine. The dentine of the basal plate becomes calcified. The maplighian layer of theepidermis in contact with the dermal papilla is known as enamel organ, the enamel organ brings

about formation of vitrodentine over the dentine of the spine. The dermal papilla forms pulp inthe pulp cavity of the scale. The overlying epidermis moves away and also wears off so that the

spine projects above, while the basal remains embedded in the dermis.

2. Briefly compare and contrast epidermis and dermis of Cartilaginous and Bony fishes. Indicate

the characteristic feature of comparison.

Cartilaginous (class Chondrichtyes) and bony fishes (class Osteichthyes) differ in their epidermal and dermal structure and composition.

Epidermis

The epidermis of the cartilaginous fishes is mainly composed cells that are compactly

disposed and have less abundant unicellular glands. Multicellular glands are limited and present

only on restricted areas, like at the base of the claspers of males. While in bony fishes, the

epidermal glands are mainly composed of unicellular mucous gland that produces mucous on the

surface of its skin. Although, some species have few multicellular glands in some parts of their

body; these are sometimes used to impede desiccations.

Dermis

In cartilaginous fishes, the dermis is thicker than the epidermis and is composed of two

more layers. The dermis of the cartilaginous fish is mostly composed of placoid scales. These

placoid scales have spines that penetrate the epidermis causing it to have a sandpaper-like

texture. This structure is denser on its dorsal side, compared to its ventral part. While in bony

fishes, the dermis is characterized by the presence of ganoid scales, cycloid scales or the ctenoid

scales.

3. What are the exteroreceptive roles of the integuments? Briefly describe each.

There are many types of exteroreceptors that can be present in the integuments of an

organism. These receptors are usually found on the dermis or epidermis. The exteroreceptive role

of the integuments depends on the type of receptor that is present in its epidermis or dermis. The

following are the receptors that are commonly found on the integuments of the organisms.



Cutaneous Mechanoreceptor

These receptors are free nerve endings that are found on the skin of an animal. This type

of exteroceptor has a common function; like detection of tension, change in texture, rapid

vibration, touch and pressure.

Thermoreceptor

A thermoreceptor is a sensory receptor, or more accurately the receptive portion of a

sensory neuron, that codes absolute and relative changes in temperature, primarily within the

innocuous range.

Nociceptor

A nociceptor is a sensory receptor that responds to potentially damaging stimuli by

sending nerve signals to the spinal cord and brain. This process, called nociception, usually

causes the perception of pain.

Chemoreceptor

A chemoreceptor, also known as chemosensor, is a sensory receptor that transduces a

chemical signal into an action potential. In more general terms, a chemosensor detects certain

chemical stimuli in the environment.

shark activity 1

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